From georg@nlp.physik.th-darmstadt.de Wed May  4 12:37:08 1994
Date: Wed, 4 May 94 12:19:50 +0200
From: Georg Mueller <georg@nlp.physik.th-darmstadt.de>
To: analogue@magnus.acs.ohio-state.edu
Subject: Wavetables (was: Vector synths)


A WaveTable consists of up to 61 different Waves (00..60) plus tri,
sqr and saw. There are 
	(000..245) Rom-Waves, 
	(246..306) internal UserWaves,
	(307..367) Card Waves and
	(368..505) Rom-Waves, new with V2.0.

A Wave consists of 64 Bytes (8-Bit), thats the positive cycle.

The Wave(Control)Tables are
	(00..27) Rom-Tables,
	(28..31) arithmetically generated,
	(32..43) internal User Ram-Tables,
	(44..55) Card-Ram Tables,
	(56..74) arithmetically generated, new with V2.0 and
        (75..87) ROM tables, new with V2.0.


In the WaveTable you select the Waves, that should sound. There are 61 
free positions, but you must only specify valid Wave for pos 0 and 60. 
For the others you assign -1. So the MicroWave interpolates in between.

Example:
POS  0   1   2   3 .. 20   21  22 .. 59   60  61  62  63
WAV 256 -1  -1  -1    -1  257  -1    -1  258  -1  -1  -1

I took an oscillograph and looked at the way the uW plays and
interpolates the Waves. For simplicity lets assume a Wave has 8 Nibbles
(4-Bit), a WaveTable has 4 free positions plus tri, sqr and saw.

Wave 1:  -_                 Wave 2:
           -_
             -_
               -_                   ________

         76543210                   00000000

That's what the uW spits out:

Wave 1:  -_      -_         Wave 2:         --------
           -_      -_
             -_      -_
               -_      -_           ________

         7654321076543210           0000000077777777

For the first half of the period the uW simply sends the number from the
Wave to the DAC. For the second half it reverses the readout direction
and sends the difference between the maximum value and the actual number.

Now lets investigate the spectral interpolation. Consider this WaveTable

POS   0   1   2   3   4   5   6
WAV   1  -1  -1   2  -1  -1  -1

We get:

-_      -_                -__               --___            --------
  -_      -_      -_         -__                 ---
    -_      -_      --_         -_  ___
      -_      -_       --_             ---__          ________

7654321076543210  5433211076654432  2221110077666555  0000000077777777

Well, that's simple linear interpolation. Marketing Hype: "Spectral"

	Georg.